1. Field of the Invention
The present invention relates to a wiring board having code information with which it is possible to recognize, for example, product number and production history of the wiring board. The present invention also relates to a method for recognizing the code information about the wiring board.
2. Description of the Related Art
A compact wiring board for mounting a semiconductor element such as a semiconductor integrated circuit element is known as a wiring board. This type of wiring board is described in, for example, Japanese Unexamined Patent Publication No. 2005-167235. The compact wiring board is obtained by disposing a wiring conductor on the inside and surface of an insulating board having thereon a plurality of insulating layers laminated one upon another. The insulating layers are formed of a heat resistant electrical insulating material, for example, a thermosetting resin, such as epoxy resin. The wiring conductor is formed of a satisfactorily conductive material, such as copper.
A mounting portion for mounting a semiconductor element is disposed at a central portion on an upper surface of the insulating board. A plurality of circular semiconductor element connection pads formed of a part of the wiring conductor are arranged in a lattice pattern on the mounting portion. An electrode terminal of the semiconductor element is connected to the semiconductor element connection pads by flip-chip connection.
An external connection surface to be connected to an external electrical circuit board is formed on a lower surface of the insulating board. A plurality of circular external connection pads formed of a part of the wiring conductor are arranged in a lattice pattern over approximately the entire surface of the external connection surface. These external connection pads are connected to a wiring conductor of the external electrical circuit board with solder interposed therebetween. The semiconductor element connection pads and the external connection pads are electrically connected to each other in predetermined pairs with the wiring conductor lying inside the insulating board interposed therebetween.
In the wiring board as described above, the semiconductor element is mounted on the mounting portion, and the electrode terminal of the semiconductor element and the semiconductor element connection pads are flip-chip connected to each other. Thereafter, the semiconductor element is packaged by filling an insulating resin called under fill between the semiconductor element and the wiring board so as to establish a seal therebetween. The external connection pads of the wiring board having the semiconductor element packaged therein are connected to the wiring conductor of the external electrical circuit board with the solder interposed therebetween. Thus, the semiconductor element is electrically connected to the external electrical circuit board.
The compact wiring board may in some cases have code information for perceiving product number and production history of the wiring board. The code information is applied by, for example, forming a two-dimensional bar code on a surface of the wiring board by laser processing or the like. When forming the two-dimensional bar code on the surface of the wiring board by laser processing, an aggregation of dots constituting the two-dimensional bar code is disposed at a portion of the surface of the insulating board which is free of the wiring conductor. The code information is to be recognized by reading the aggregation of dots with an image recognition device.
However, the downsizing and higher-density wiring of the wiring board in recent years has made it difficult to satisfactorily ensure an area necessary to dispose the two-dimensional bar code as the aggregation of dots at the portion of the surface of the insulating board. It is also difficult to impart a high contrast to the two-dimensional bar code formed on the surface of the insulating board by laser processing. Consequently, the two-dimensional bar code may not be surely recognized with the image recognition device depending on the material and color tone of the insulating board, or laser processing conditions.